In trains operated in recent years, gathering, monitoring and control of train information of vehicle-borne device on each car, for example, doors, air-conditioner, brake, motor, ATO (automatic train operator), SIV (static inverter as auxiliary power source), automatic broadcasting device and the like, is generally performed for the purpose of more comfortable operation and efficient and safe operation, and for the purpose of quick recovery from an accident, trouble or the like, if any. A digital transmission line is used to gather, monitor and control this train information. Since the recent network technique enables application of a large-capacity digital transmission line, it is possible to distribute other information than the above-described train information, for example, image information and the like.
Recently, in addition to the above-described monitoring and control that is necessary for train operation, it is also planned and partly carried out to gather, distribute and monitor forward video images and rear video images of trains and video images of platforms of stations for safer operation, and to display characters, dynamic images and static images on a display panel provided in each car in order to provide information that should be provided to passengers with respect to train operation, for example, status information when the arrival time is changed or the operation is disrupted, and various services such as weather forecast, news and advertisement. It is contemplated to provide Internet connection services mainly in mid- and long-distance trains in the future. The distribution and display of various information such as digital data and video information in trains in this manner will obviously become much more necessary, and amenities including visibility, easiness in viewing and the like, as well as improvement in its efficiency, reliability and real-time characteristic, must be considered.
In a conventional video information distribution and display system, a static image is transmitted in the form of digital static image video information processed (hereinafter referred to as compressed) to reduce the data volume. In a display device, a video image to be displayed is recognized using an image control signal, and if the video image is a static image, the state before the processing of the compressed static image video information is restored (hereinafter referred to as extraction), then stored in a display storage part, and subsequently displayed. When a video image that is currently displayed is a static image, the image is displayed using the display storage part where the static image video information is stored. Therefore, as a matter of course, the image cannot be displayed while the next static image video information to be displayed is being extracted and stored into the display storage part. This period is a blank period (see, for example, Patent Reference 1.
Patent Reference 1: JP-A-2002-209193
In this conventional system, compressed digital static image video information and an image control signal are digitally transmitted using an already installed train information device and transmission line, whereas a dynamic image is distributed to and displayed on the display device by analog transmission. The reason for this is as follows. Recently, a static image such as photograph is often picked up, edited and transmitted as digital data, and transmitting and displaying digital data as it is, is more efficient than carrying out analog conversion. Moreover, though high resolution of approximately XGA (1024×768) is necessary for sharply displaying a static image containing a large number of characters in small font, such as photograph or magazine advertisement, data compression allows approximately 100 to 200 K transmission bytes per image. If the conventionally employed transmission system (packet system) is utilized for linkage between train information devices, static image video information of high resolution can be distributed at a low cost.
Meanwhile, in the case of a dynamic image that is displayed at a high speed of 30 frames per second, the resolution equivalent to that of a static image is not necessary and resolution of approximately 480×320 suffices. Transmission of dynamic image video information according to the digital data system is technically possible. However, particularly the modulation and demodulation mechanism is complicated, and at the present stage, the analog transmission system is suitable as the dynamic image distribution system for the video information distribution and display system in trains because of the high cost.
In the display device, when displaying a static image based on an incoming image control signal, compressed data is extracted and subsequently displayed, as a matter of course.